This invention relates to a filtering device for making brewed beverages. Furthermore, a second invention relates to the filter element insertable into the filtering device referred to above. Finally, a third invention relates to the method necessary for manufacturing the filter element.
From U.S. Pat. No. 3,089,405 there is already known a filtering device for a coffee maker serving to prepare brewed beverages. The filtering device is comprised of a ring-like portion of a water pipe, briefly referred to as ring pipe, on the outside of which a filter sack is freely suspended. The filter sack is adapted to be filled with coffee grounds, and hot water can be introduced through the filter sack's mouth for the purpose of filtration. The hot water entering through the open end of the annular water pipe, upon taking up extractive substances from the extractable material (process of extraction), is drained freely along the outer wall of the filter sack to be received in a container placed underneath.
For installation, the filter sack is secured to the filter support using holding means. For this purpose, an elastic band or an elastic string is drawn into the filter sack's upper end, which band or string, together with the mouth of the filter sack, is pulled from outside around the ring pipe configured as the filter support. After the widened mouth of the filter sack above the ring pipe is released, the elastic string will be shirred in such a way that the diameter of the filter sack above the ring pipe becomes smaller than the section around the ring pipe. In this manner, the filter sack is secured to the ring pipe and hence prevented from falling down during the brewing cycle.
Aside from the relatively complicated procedure of securing the filter sack upon the ring pipe--requiring the mouth of the filter sack to be opened by pulling the elastic string apart until the sack can be fitted over the outer surface of the ring pipe from below--, a highly elaborate process is involved to draw an elastic band or an elastic string into the upper end portion of the filter sack to make sure that the elastic string secures the filter element on the filter support.
Such securing of a filter sack to a filter support of a beverage brewing apparatus is an elaborate and complicated procedure depending ultimately on the operator's skills in opening the mouth of the filter element, fitting it over the ring pipe, and subsequently aligning the filter element on the filter support to make sure that the longitudinal axis of the filter element extends essentially perpendicularly; in the event of an improper installation, the paper filter sack tends to be askew, to tear and/or even detach itself from the filter support, entailing the risk of an operator scalding himself or herself.
The need to use an elastic string or rubber band fitted to the filter element as an extra addition and the elaborate assembly of this rubber band to the filter sack is far from comfortable and adds to the unit price of the filter sack, which makes itself felt clearly in particular in cases where coffee is brewed several times a day. Such mounting of a filter sack is in all likelihood only suitable for use where the sack itself is made of a stable filter material.
Furthermore, from EP-A-0 741 988 a filtering device is known in which the filter element is assembled from two shell-shaped paper strips to form a single piece. In the area of its mouth the filter element has a free rim which is folded over such as to form a pocket. The pocket opens in downward direction, extending essentially in the direction of the wall of the receiving area. The filter support comprises a substantially round section of a circle bent from wire and having bent thereon a wire-shaped holder and a stud member at the opposite ends. The semicircular sections of the holder serve to hold the filtering device, while the diametrically opposite supporting sections serve to support the filtering device on the rim of a vessel.
If in this filtering device the ring member is not accurately at the deepest point of the pocket, that is, at the location where the rim is folded towards the filter body, it cannot happen that the rim opens upwardly causing the filter element to fall down due to its weight increase as the water slowly penetrates the coffee grounds, the receiving cavity and in consequence also the rim of the filter element during the brewing cycle, because the filter layers and the rims are made of a composite fabric of heat-sealable fibers or similar woven fabrics, these elements being even connected by heat sealing this composite fabric or by similar means. The costs for such a filter element made of a composite fabric are however, considerable, particularly when this filter element is intended for use as a disposable filter involving high quantities. When used as reusable filter the same cost considerations apply as mentioned in the foregoing.
From DE-40 38 023 A1 a method of manufacturing a two- or multi-shell container from paperboard or a similar material is known as described in the prior-art portion of patent claim 31. In this method, the paper, also referred to as the blank, is drawn from the edge side of the die half in addition to being drawn from the blank side while further material is fed. In this process, stock present between the two die halves is available to compensate for the forming of the paper in the die cavity, without the material being subjected to excessive strain. In this method, therefore, a receptacle is formed by feeding in stock.
From U.S. Pat. No. 5,171,457, in particular from FIG. 6, a rimmed coffee filter container cup is known into which an equally rimmed coffee filter is insertable in accordance with FIG. 7. In this arrangement, the rim of the coffee filter takes support upon the rim of the coffee filter container cup. The cylindrical wall of the cup-shaped coffee filter has exposed ruffles shaped in a zigzag configuration and oriented outwardly. The exposed ruffles continue in the rim extending at approximately right angles to the cylindrical wall by being apparently pressed together in the rim.
Finally, from FR-A-2 691 059 a filter cartridge made of filter paper is known whose mouth is provided with a rim extending away from the filter cartridge at approximately right angles thereto. The mouth of the filter cartridge is closed with a filter paper lid extending over the rim. The rim ensures a perfect position of the filter cartridge in the interior of a metal filter of a coffee maker.